Your previous post:
probably seems like a different topic to you...but as you understand conditional privileges, you'll find that they work in a number of ways.
Please see the answer in your other post (link above) and use the "limited..." calculation of
Measurement1 - Measurement2 >= 1 ("greater than or equal to" intended)
or whatever other calculation best describes the situation where the user CAN edit the field.
Then take a breather and think of all the awesome ways conditional privileges can be used to help you (and royally P.O. the next person who has to support the database in day to day operations...don't go overboard, just use what is needed)
Enjoy the July 4th holiday if it applies!